4-(4,4,5,5-tetramethyl-1,3-dioxide) imidazolyl-1-benzoic acid (NIT-Ph-p-BEN nitroxide radicals) was synthesized by a facile condensation reaction using 4-formylbenzoic acid and 2,3-bis(hydroxylamino)-2,3-dimethylbutane as precursors, and NaIO4 as oxidant. The product was characterized by FT-IR, UV, ERP and elemental analysis. The oxidative degradation activity of the NIT-Ph-p-BEN nitroxide radicals was investigated by catalytic degradation of organic dyes methyl orange, methyl blue and rhodamine B in wastewater. The results show that when the concentration of methyl orange, methyl blue and rhodamine B was 15 mg/L, and the concentration of NIT-Ph-p-BEN and H2O2 were 0.15 g/L and 30 mmol/L, respectively, NIT-Ph-p-BEN exhibited the best degradation activity for methyl orange. The degradation rate of methyl orange reached 94.26% only within 1 h. The catalytic mechanism demonstrated that NIT-Ph-p-BEN nitroxide radicals were effectively activated and regenerated by H2O2.